50 killed in Orlando massacre, worst mass shooting U.S. history

The mayor of Orlando says there were 50 casualties and there are 53 more hospitalized after a mass shooting at a popular gay nightclub there in what has become the worst mass shooting in United States history.

"There's blood everywhere," Mayor Buddy Dyer said Sunday at a news conference, hours after the shooting.

He says the shooter used an assault rifle on all those killed.

Earlier, U.S. Rep. Alan Grayson identified the shooter as Omar Mateen of Port St. Lucie, Florida. He cited law enforcement officials in speaking to reporters.

A federal law enforcement official with knowledge of the investigation also identified him. The official was not authorized to discuss the investigation publicly and spoke on condition of anonymity.

Florida Department of Law Enforcement Special Agent in Charge Danny Banks said earlier that the mass shooting is being investigated as an act of terrorism. He says authorities are looking into whether the incident was an act of domestic or international terror, and if the shooter was a lone wolf.

Gov. Rick Scott says in a statement Sunday, hours after the incident, that thoughts and prayers are with the victims and their families.

The statement says he'll meet with law enforcement and local officials in Orlando.

"We will devote every resource available to assist with the shooting in Orlando. Our state emergency operations center is also monitoring this tragic incident," Scott said.

His statement also thanks the first responders.

Florida Department of Law Enforcement Special Agent in Charge Danny Banks said earlier that the mass shooting is being investigated as an act of terrorism. He says authorities are looking into whether the incident was an act of domestic or international terror, and if the shooter was a lone wolf.

President Barack Obama has been briefed by his homeland security and counterterrorism adviser about the shooting.

The White House said Sunday, several hours after the incident, that Obama has been briefed and has asked for regular updates as the FBI and other federal officials work with Orlando police on the case.

Press secretary Josh Earnest said in a statement that the president has directed federal officials to provide "any necessary assistance to pursue the investigation and support the community."